Potentiometers or variable resistor element



March 29, 1955 E. A. DE BELL POTENTIOMETERS OR VARIABLE RESISTOR ELEMENT Filed July 25, 1952 United States Patent POTENTIOMETERS OR VARIABLE RESISTOR ELEMENT Ernest Alfred De Bell, Wroughton, England, assignor to The Plessey Company Limited, Ilford, England, a British company Application July 25, 1952, Serial No. 300,907

3 Claims. (Cl. 201-55) This invention relates to potentiometers or resistor elements used in communication circuits as variable resistors, such as volume controls and time controls.

In resistance elements of the kind referred to it is customary to have a metal collector ring arranged in an insulated base, and a spring contact member is provided with metal contact button rollers or the like which make a sliding contact with the collector ring. It has been found that due to the metal to metal contact, there is an increased resistance which results in creating a noise in the communication circuit. It is an object of this invention to eliminate this defective contact resistance thereby providing a resistive device having advantageous characteristics.

An object of the invention is to eliminate or reduce to an absolute minimum any defective contact resistance thereby providing a resistive device having advantageous characteristics.

Another object of the invention is to provide the metal collector ring with a carbon brush or brushes which make a sliding contact with the metal collector ring whereby contact resistance and noise resulting therefrom is reduced to a minimum.

A further object of the invention is to fit the metal collector ring with a carbon contact in the form of a segment, stud, button roller or the like.

The invention will now be described with reference to the accompanying drawing, in which:

Fig. 1 is an exploded view of a potentiometer showing one form of carbon brush,

Fig. 2 is an elevation partly in section of a complete assembly of a potentiometer according to Fig. 1.

Fig. 3 is a detail showing another form of brush and,

Fig. 4 is a detail showing a further modified form of carbon brush.

Referring to Figs. 1 and 2:

A resistor track 1, collector ring 2 and terminal tags 3, 4, 5 are embedded in a moulded insulating base 6. The terminal tags 3 and 5 are connected to the respective ends of the resistor track 1 and the terminal tag 4 is connected to the ring 2.

A metal backing plate 7 and an externally threaded bush 8 are moulded to the base 6 on the opposite face to the resistor track 1 and collector ring 2.

A metal plate 9 with a projection 9 is riveted to the end of a shaft 10 and an insulating disc 11 mounted on the shaft 10 has a slot 12 to receive a bent projection 13 integral with the plate 9 whereby the disc can rotate with the shaft 10.

A brush holder 14 has collector prongs 15 with a dimple 16 at each end, and a contact element 17 is supported in a bent projection portion 18 formed in the brush holder A segmental non-metallic brush 19 with dimple recesses 20 for receiving the dimple ended prongs 15, is pressed against the collector ring 2 as hereinafter set forth.

In assembling, the shaft 10 is inserted through the bush 8, the brush holder 14 is fitted with a contact element 17 and the bent projection portion 18 is placed against the insulating disc 11 in such a manner that the bent projection portion 18 passes into a coinciding slot 21 and the shoulders 22 formed in the brush holder 14 serve as hinges to permit the collector prongs 15 to be at an incline with respect to the disc 11, when the-shaft 10 is rotatably secured to the bush 8 by means of a C-clip 35.

The carbon brush 19 is held in sliding contact with the collector ring 2 by means of the dimples 16 engaging the dimple recesses 20 prior to securing of the shaft 10 to the base 6. In this arrangement the brush holder 14 being hingedly mounted in the insulating disc 11 and suitably spaced from the moulded base 6 by spacing washers 23 enables the prongs 15 to press the brush 19 against the collector ring 2, and the contact element 17 against the resistor trace 1 as shown in Fig. 2.

A cover 24 having an indent 25 fits over the resistor assembly and is secured thereto by bending lugs 26 over the backing plate 7. Limitation of rotation of the shaft 10 in either direction is by the projection 9 in plate 9 abutting against the indent 25.

Referring to Fig. 3, an alternative form of brush and brush holder is provided in which the brush holder is in the form of a ring 27 with a perforatedear 28 to receive a tapered carbon slug 29. Said ring 27 has a bent projection portion 18 to support a contact element 17 in a sinailgr manner to that described with reference to Figs.

Fig. 4 shows a further modified form of brush and brush holder in which the brush holder 30 has two diametrically opposed bent projecting portions 31, 32 for receiving carbon contact brushes 33, 34 which are pressed into electrical contact with the resistor track 1 and collector ring 2 respectively. In both modifications described under Figs. 3 and 4, the brush holder is intended to be hingedly mounted so that the brushes are pressed against their respective tracks.

I claim:

1. In a resistance device having a resistor track, a metallic collector ring, and terminal tags embedded in a moulded base, a brush holder, said brush holder is formed with prongs having a dimple at each end and a bent projection portion, a segmental non-metallic brush engaged by the dimple ended prongs, a second brush located in the bent projection portion of the holder said brushes being pressed into electrical contact with the collector ring and resistor track respectively.

2. In a resistance device having a resistor track, a metallic collector ring, and terminal tags embedded in a moulded base, a brush holder in which the brush holder has a perforated ear and a bent projecting portion, a carbon slug supported in the perforated ear and a carbon brush is supported by the bent projecting portion, said carbon slug and carbon brush being pressed into electrical contact with the collector ring and resistor track respectively.

3. In a resistance device having a resistor track, a metallic collector ring, and terminal tags embedded in a moulded base, a brush holder, said brush holder constituting a spring metal ring having two diametrically opposed bent projection portions on different pitch circles a carbon brush mounted in each of the bent projection portions in said holder, said brushes being pressed into electrical contact with the resistor track and collector ring respectively.

References Cited in the file of this patent UNITED STATES PATENTS 1,717,913 Brockwag June 18, 1929 2,623,188 Tourneau et al Dec. 23, 1952 FOREIGN PATENTS 583,143 Great Britain Dec. 10, 1946 

